1. Field of the Invention
This invention relates generally to a system and method for remotely monitoring and/or controlling an apparatus and specifically to a lamp monitoring and control system and method for use with street lamps. The present invention includes a monitoring and control unit, such as the lamp monitoring and control unit disclosed in co-pending application entitled "LAMP MONITORING AND CONTROL UNIT AND METHOD", Ser. No. 08/838,302, the contents of which are incorporated herein by reference.
2. Background of the Related Art
The first street lamps were used in Europe during the latter half of the seventeenth century. These lamps consisted of lanterns which were attached to cables strung across the street so that the lantern hung over the center of the street. In France, the police were responsible for operating and maintaining these original street lamps while in England contractors were hired for street lamp operation and maintenance. In all instances, the operation and maintenance of street lamps was considered a government function.
The operation and maintenance of street lamps, or more generally any units which are distributed over a large geographic area, can be divided into two tasks: monitor and control. Monitoring comprises the transmission of information from the distributed unit regarding the unit's status and controlling comprises the reception of information by the distributed unit.
For the present example in which the distributed units are street lamps, the monitoring function comprises periodic checks of the street lamps to determine if they are functioning properly. The controlling function comprises turning the street lamps on at night and off during the day.
This monitor and control function of the early street lamps was very labor intensive since each street lamp had to be individually lit (controlled) and watched for any problems (monitored). Because these early street lamps were simply lanterns, there was no centralized mechanism for monitor and control and both of these functions were distributed at each of the street lamps.
Eventually, the street lamps were moved from the cables hanging over the street to poles which were mounted at the side of the street. Additionally, the primitive lanterns were replaced with oil lamps.
The oil lamps were a substantial improvement over the original lanterns because they produced a much brighter light. This resulted in illumination of a greater area by each street lamp. Unfortunately, these street lamps still had the same problem as the original lanterns in that there was no centralized monitor and control mechanism to light the street lamps at night and watch for problems.
In the 1840's, the oil lamps were replaced by gaslights in France. The advent of this new technology began a government centralization of a portion of the control function for street lighting since the gas for the lights was supplied from a central location.
In the 1880's, the gaslights were replaced with electrical lamps. The electrical power for these street lamps was again provided from a central location. With the advent of electrical street lamps, the government finally had a centralized method for controlling the lamps by controlling the source of electrical power.
The early electrical street lamps were composed of arc lamps in which the illumination was produced by an arc of electricity flowing between two electrodes.
Currently, most street lamps still use arc lamps for illumination. The mercury-vapor lamp is the most common form of street lamp in use today. In this type of lamp, the illumination is produced by an arc which takes place in a mercury vapor.
FIG. 1 shows the configuration of a typical mercury-vapor lamp. This figure is provided only for demonstration purposes since there are a variety of different types of mercury-vapor lamps.
The mercury-vapor lamp consists of an arc tube 110 which is filled with argon gas and a small amount of pure mercury. Arc tube 110 is mounted inside a large outer bulb 120 which encloses and protects the arc tube. Additionally, the outer bulb may be coated with phosphors to improve the color of the light emitted and reduce the ultraviolet radiation emitted. Mounting of arc tube 110 inside outer bulb 120 may be accomplished with an arc tube mount support 130 on the top and a stem 140 on the bottom.
Main electrodes 150a and 150b, with opposite polarities, are mechanically sealed at both ends of arc tube 110. The mercury-vapor lamp requires a sizeable voltage to start the arc between main electrodes 150a and 150b.
The starting of the mercury-vapor lamp is controlled by a starting circuit (not shown in FIG. 1) which is attached between the power source (not shown in FIG. 1) and the lamp. Unfortunately, there is no standard starting circuit for mercury-vapor lamps. After the lamp is started, the lamp current will continue to increase unless the starting circuit provides some means for limiting the current. Typically, the lamp current is limited by a resistor, which severely reduces the efficiency of the circuit, or by a magnetic device, such as a choke or a transformer, called a ballast.
During the starting operation, electrons move through a starting resistor 160 to a starting electrode 170 and across a short gap between starting electrode 170 and main electrode 150b of opposite polarity. The electrons cause ionization of some of the Argon gas in the arc tube. The ionized gas diffuses until a main arc develops between the two opposite polarity main electrodes 150a and 150b. The heat from the main arc vaporizes the mercury droplets to produce ionized current carriers. As the lamp current increases, the ballast acts to limit the current and reduce the supply voltage to maintain stable operation and extinguish the arc between main electrode 150b and starting electrode 170.
Because of the variety of different types of starter circuits, it is virtually impossible to characterize the current and voltage characteristics of the mercury-vapor lamp. In fact, the mercury-vapor lamp may require minutes of warm-up before light is emitted. Additionally, if power is lost, the lamp must cool and the mercury pressure must decrease before the starting arc can start again.
The mercury-vapor lamp has become one of the predominant types of street lamp with millions of units produced annually. The current installed base of these street lamps is enormous with more than 500,000 street lamps in Los Angeles alone. The mercury-vapor lamp is not the most efficient gaseous discharge lamp, but is preferred for use in street lamps because of its long life, reliable performance, and relatively low cost.
Although the mercury-vapor lamp has been used as a common example of current street lamps, there is increasing use of other types of lamps such as metal halide and high pressure sodium. All of these types of lamps require a starting circuit which makes it virtually impossible to characterize the current and voltage characteristics of the lamp.
FIG. 2 shows a lamp arrangement 201 with a typical lamp sensor unit 210 which is situated between a power source 220 and a lamp assembly 230. Lamp assembly 230 includes a lamp 240 (such as the mercury-vapor lamp presented in FIG. 1) and a starting circuit 250.
Most cities currently use automatic lamp control units to control the street lamps. These lamp control units provide an automatic, but decentralized, control mechanism for turning the street lamps on at night and off during the day.
A typical street lamp assembly 201 includes a lamp sensor unit 210 which in turn includes a light sensor 260 and a relay 270 as shown in FIG. 2. Lamp sensor unit 210 is electrically coupled between external power source 220 and starting circuit 250 of lamp assembly 230. There is a hot line 280a and a neutral line 280b providing electrical connection between power source 220 and lamp sensor unit 210. Additionally, there is a switched line 280c and a neutral line 280d providing electrical connection between lamp sensor unit 210 and starting circuit 250 of lamp assembly 230.
From a physical standpoint, most lamp sensor units 210 use a standard three prong plug, for example a twist lock plug, to connect to the back of lamp assembly 230. The three prongs couple to hot line 280a, switched line 280c, and neutral lines 280b and 280d. In other words, the neutral lines 280b and 280d are both connected to the same physical prong since they are at the same electrical potential. Some systems also have a ground wire, but no ground wire is shown in FIG. 2 since it is not relevant to the operation of lamp sensor unit 210.
Power source 220 may be a standard 115 Volt, 60 Hz source from a power line. Of course, a variety of alternatives are available for power source 220. In foreign countries, power source 220 may be a 220 Volt, 50 Hz source from a power line. Additionally, power source 220 may be a DC voltage source or, in certain remote regions, it may be a battery which is charged by a solar reflector.
The operation of lamp sensor unit 210 is fairly simple. At sunset, when the light from the sun decreases below a sunset threshold, light sensor 260 detects this condition and causes relay 270 to close. Closure of relay 270 results in electrical connection of hot line 280a and switched line 280c with power being applied to starting circuit 250 of lamp assembly 230 to ultimately produce light from lamp 240. At sunrise, when the light from the sun increases above a sunrise threshold, light sensor 260 detects this condition and causes relay 270 to open. Opening of relay 270 eliminates electrical connection between hot line 280a and switched line 280c and causes the removal of power from starting circuit 250 which turns lamp 240 off.
Lamp sensor unit 210 provides an automated, distributed control mechanism to turn lamp assembly 230 on and off. Unfortunately, it provides no mechanism for centralized monitoring of the street lamp to determine if the lamp is functioning properly. This problem is particularly important in regard to the street lamps on major boulevards and highways in large cities. When a street lamp burns out over a highway, it is often not replaced for a long period of time because the maintenance crew will only schedule a replacement lamp when someone calls the city maintenance department and identifies the exact pole location of the bad lamp. Since most automobile drivers will not stop on the highway just to report a bad street lamp, a bad lamp may go unreported indefinitely.
Additionally, if a lamp is producing light but has a hidden problem, visual monitoring of the lamp will never be able to detect the problem. Some examples of hidden problems relate to current, when the lamp is drawing significantly more current than is normal, or voltage, when the power supply is not supplying the appropriate voltage level to the street lamp.
Furthermore, the present system of lamp control in which an individual light sensor is located at each street lamp, is a distributed control system which does not allow for centralized control. For example, if the city wanted to turn on all of the street lamps in a certain area at a certain time, this could not be done because of the distributed nature of the present lamp control circuits.
Because of these limitations, a new type of lamp monitoring and control system is needed which allows centralized monitoring and/or control of the street lamps in a geographical area.
One attempt to produce a centralized control mechanism is a product called the RadioSwitch made by Cetronic. The RadioSwitch is a remotely controlled time switch for installation on the DIN-bar of control units. It is used for remote control of electrical equipment via local or national paging networks. Unfortunately, the RadioSwitch is unable to address most of the problems listed above.
Since the RadioSwitch is receive only (no transmit capability), it only allows one to remotely control external equipment. Furthermore, since the communication link for the RadioSwitch is via paging networks, it is unable to operate in areas in which paging does not exist (for example, large rural areas in the United States). Additionally, although the RadioSwitch can be used to control street lamps, it does not use the standard three prong interface used by the present lamp control units. Accordingly, installation is difficult because it cannot be used as a plug-in replacement for the current lamp control units.
Because of these limitations of the available equipment, there exists a need for a new type of lamp monitoring and control system which allows centralized monitoring and/or control of the street lamps in a geographical area. More specifically, this new system must be inexpensive, reliable, and able to handle the traffic generated by communication with the millions of currently installed street lamps.
Although the above discussion has presented street lamps as an example, there is a more general need for a new type of monitoring and control system which allows centralized monitoring and/or control of units distributed over a large geographical area.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.